Injection molding know-how and maybe machine access?

[Kyle B.]

Hi,

I'm currently kicking around some ideas for a technology at my workplace and the question of what's possible with injection molding came up.

I don't know that much about it...

I'm curious about the possibilities of encapsulating some electronics (a PCB with a lot of surface mount components) and possibly a pre-charged Li-ion battery in some kind of plastic ball so that they can survive being tossed around and having high pressures applied.

Is there anyone on this list who knows a bit about this sort of thing and would be happy to answer some questions for me? :)

Furthermore, I've seen some fairly compact-looking injection molding machines on youtube/etc. and was wondering if any open spaces had such machines. I don't think there's anything like this at Meadowbank... but maybe someone has some old kit somewhere?

Anyone have any suggestions? :)

Cheers,

  Kyle

[Patrick Barnes]

Hi Kyle,

Can't claim any special experience... but;

1. Potting/encapsulating electronics sounds more like a resin/casting thing than injecion molding.

2. Lipoly + heat is something to be very wary of, as is lipoly + pressure. (Also +shock, and probably a few other things. And 1% chance of something wrong × 1000 units... )

3. Like so many things, the full answer will start with "it depends." How many units? Li ion is a hard req or button cells will do? Is bounciness an issue, is surface finish an issue? How many times does it have to survive shocks? How large, how much power is needed, how long does it need to last?

I have seen some interesting work done by members on 3d printing hollow shells, then filling with resin to make a hard, solid and strong part. (The shell stays on)
Maybe you could try the same, even with silicone if bounciness is needed?

Sounds like a fun project!

-Patrick

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[Darryl Adams]

Injected molded plastic is quite brittle. However the biggest issue is the mold. The benefit of injection molding is non decaying of the mold as it is metal rather than latex or rubber used in resin or pewter molding

[Matt Callow]

Brittle? Doesn't that depend on the type of plastic used? Yogurt pots are injection molded, and I wouldn't class them as brittle.

On 21 May 2016 9:49 am, "Darryl Adams" <vora...@gmail.com> wrote:

Injected molded plastic is quite brittle. However the biggest issue is the mold. The benefit of injection molding is non decaying of the mold as it is metal rather than latex or rubber used in resin or pewter molding

[Kris]

I thought they were blown

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[Kris]

Ah, depends, some are some aren't

http://support.grantadesign.com/resources/selector/14/en/indepth/html/indepth/processinfo/processcasestudy_yoghurtpot.htm

[Matt Callow]

I was about to quote the same site!

[Ada Lim]

On Sat, May 21, 2016 at 9:49 AM, Darryl Adams <vora...@gmail.com> wrote:
> Injected molded plastic is quite brittle. However the biggest issue is the mold. The benefit of injection molding is non decaying of the mold as it is metal rather than latex or rubber used in resin or pewter molding

I wouldn't call injection moulded PP brittle.

-A

[Darryl Adams]

I was thinking of the traditional airfix models style. Much of the wargaming plastic I use don't take much punishment unless they are solid. PET is of cause flexible.

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[Julian Sortland]

I have seen designers on TV pay about $20k to have the moulds made!

My dad worked at Rheem in Hornsby, now closed, where they made plastic bottles.  It is certainly a process for large volumes, such as Parmolive detergent bottles.

Julian.

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[Ada Lim]

On Sun, May 22, 2016 at 6:53 AM, Darryl Adams <vora...@gmail.com> wrote:
> I was thinking of the traditional airfix models style. Much of the wargaming
> plastic I use don't take much punishment unless they are solid. PET is of
> cause flexible.

none of which is polypropylene.

on the other hand, something like
http://www.ikea.com/us/en/catalog/products/40267554/ is made of
injection moulded polypropylene.

Perhaps the problem is that, like valvoline, plastics ain't plastics.
I think you are conflating the material with the process.

Also, I wonder whether lmwtfy should be as much of a thing as lmgtfy.

There are the usual exhortations toward economy and precision of
language - so if you write

"Injection moulded plastic is quite brittle"

This can mean

A. "There exists a brittle plastic which can be injection moulded"
B. "There exists a plastic which becomes brittle when injection moulded"
C. "All plastics become brittle when injection moulded"

Your particular statement implies (C) when it seems that what you mean
is (A). Polystyrene is, to a large extent, brittle - consider CD
cases. Polypropylene is a counter example to (C) - the hinge from a
Tic-Tac box is injection moulded, yet is almost the opposite of
brittle.

(caveat: my knowledge of polymers is not particularly thorough or
well-founded.)